Photos: Soaring ambition for solar aircraft

The Solar Impulse HB-SIA is designed to fly both day and night without the need for fuel and without producing any pollution.

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Solar Impulse HB-SIA

On June 26, a prototype of the world's latest solar-powered airplane was unveiled at an airfield in Dubendorf, Switzerland, by company co-founders and future pilots Bertrand Piccard and André Borschberg.

The Solar Impulse HB-SIA is designed to fly both day and night without the need for fuel and without producing any pollution. The plane, which is scheduled to make its first flight later this year, was built to stay airborne for several days operating just on the power emitted by the sun and captured by its solar panels. The goal and challenge of the craft is to show the viability of renewable energy.

"If an aircraft is able to fly day and night without fuel, propelled solely by solar energy," says Piccard, "let no one come and claim that is impossible to do the same thing for motor vehicles, heating and air conditioning systems, and computers."

Wingspan

The wingspan of the Solar Impulse HB-SIA stretches to more than 200 feet, equal to that of a Boeing 747.

The long wingspan, like that of a glider, boosts the plane's aerodynamic efficiency by decreasing drag, thereby lessening the power required by the electric motors to keep the HB-SIA in the air. This reduces the craft's sink rate, the speed at which it descends to the ground, to guard against too hard a landing.

Under the wing are four small pods, each containing a motor, a polymer lithium battery, and a system to regulate the charge and discharge of each battery. Thermal insulation helps conserve the heat generated by the batteries and keeps them running at an optimal temperature, according to Solar Impulse.

An on-board computer will constantly analyze the flight parameters, providing the pilot with the information needed to make key decisions. The computer will also send data to the ground team and regulate power to the electric motors. Through this technical chain of events, the HB-SIA will automatically handle course corrections and conserve the amount of energy consumed.

Solar panels

The huge wing boasts more than 12,000 solar panels. In creating the panels, the designers had to balance weight with efficiency. The energy soaked up by the panels serves to propel the plane. But those panels also charge the plane's lithium polymer batteries, allowing it to take flight at night. The pilots can count on at best only eight hours of sunlight per day, and the lower the sun sinks on the horizon, the less light there is to be captured by the panels.

When the Solar Impulse HB-SIA begins its first lengthy test flight throughout the day and night, the pilots must hope the batteries have enough energy to keep it in the air until the sun comes up the next morning to recharge the panels.

Carbon fiber skeleton

To stay light yet rigid, the HB-SIA is built with a skeleton structure using a carbon fiber composite. The underbelly of the wing is covered with a flexible film, while 120 carbon fiber ribs are set up between the upper and lower portions of the wing. These ribs help give the plane its aerodynamic shape.

Virtual flight

Two virtual flights were conducted using Solar Impulse simulators, one in 2007 and another in 2008. For the 2008 "flight," both Piccard and Borschberg were the test subjects, each spending 25 hours flying nonstop in a cockpit just like the one in the Solar Impulse. Equipped with their helmets, parachutes, oxygen masks, and food supplies, the two pilots were able to test the cockpit's ergonomics, the aerodynamics of the flight, and the efficiency of the batteries during nighttime.

Five screens set up around the cockpit gave the pilot the feel of a real flight.

"I went into a simulator and came back out of an airplane," said Piccard after the 25-hour simulation. "This proves to what extent the simulation is fascinating."

Bertrand Piccard

Solar Impluse founder and pilot Bertrand Piccard began his eclectic career as a psychiatrist specializing in hypnotherapy. That led to an interest in how humans behave under extreme conditions. From there, he became involved in ballooning and won the first transatlantic balloon race before starting his famous Breitling Orbiter project. Piloting the Orbiter 3 in 1990, he made the first nonstop, round-the-world balloon flight, setting a record for the longest flight in the history of air travel.

Using the money he won for his historic Orbiter flight, Piccard started the humanitarian foundation Winds of Hope, which tries to combat deadly childhood diseases in poor countries.

Piccard family

Adventure and exploration seem to be in the family DNA for Piccard, shown here as a child with his father and grandfather.

Grandfather Auguste Piccard devised the principles behind both the stratospheric balloon and the pressurized cabin. Flying a pressurized, hydrogen-filled balloon into the stratosphere, he reached an altitude of 15,780 meters, or 51,771 feet, in 1931 and 16,201 meters, or 53,152 feet, in 1932. Using the same concept of pressurization, he later invented a submarine called the Bathyscaphe Trieste, and in 1953, dove beneath the sea with his son Jacques to a depth of 3,150 meters, or 10,334 feet.

Jacques Piccard followed in the family footsteps by developing underwater vehicles to study the ocean depths. Traveling in the Bathyscaphe Trieste, he and co-pilot Lt. Don Walsh are still the only two people to have reached the deepest point underwater, diving to a distance of 10,916 meters, or 35,813 feet, in 1960. He later explored the Gulf Stream with another submersible vessel that he invented. Piloting the mesoscaphe Ben Franklin, he and his crew stayed underwater for a month, providing a test study for the effects of such a lengthy journey on human beings. NASA has long incorporated research from this mission in planning its space flights.

Andre Borschberg

Solar Impulse co-founder and co-pilot André Borschberg, was fascinated by aviation as a child. Trained to fly at the Swiss Air Force School, he has professional licenses to pilot both airplanes and helicopters.

As a mechanical engineer and MIT graduate in management science, Borschberg has also started and managed several companies, including a risk capital venture and two technology firms. Like Piccard, he's devoted himself to social causes and has worked on behalf of Restos du Coeur (Restaurants of the Heart), a French charitable group that distributes food to the poor and homeless.

Solar Impulse team

A team of 70 people worked for more than six years performing the many calculations, simulations, and tests to complete the final aircraft. Construction of the Solar Impulse HB-SIA prototype began in June 2007 and further work will continue throughout the summer of 2009.

To build the prototype, a subteam of 50 specialists, aided by close to 100 external advisers, combined their knowledge and expertise. The plane had to be constructed to satisfy the needs of the designers, equipment suppliers, and pilots. Extensive research and testing were done in such areas as aerodynamics, energy efficiency, mechanical structure, and manufacturing processes.

Here the entire Solar Impulse team lines up at the Dubendorf construction facility in which the Solar Impulse was assembled.

News conference

The Solar Impulse HB-SIA is unveiled to the public and the press at a news conference on June 26. Here, Piccard and Borschberg open the curtain on the solar-powered plane before a crowd of 800 people, including Prince Albert II of Monaco, the Swiss Minister of Energy and Environment, the CEOs of sponsors Solvay, Omega, and Deutsche Bank, and the CEO of the International Air Transport Association.

Artist's impression

After further refinements on the ground, the Solar Impulse is scheduled to make its first test flights by the end of 2009. The first flight will see the plane launch from its current home at the Dubendorf airport; the second will see it take off from the Payerne air base less than two hours away.

The aircraft will then take its first night test flight in 2010 to see if it can stay in the air for a 36-hour day-night-day cycle running solely on battery power without any fuel. From there, the next generation of the Solar Impulse, the HB-SIB, will make two test flights in 2012--the first across the Atlantic, and the second around the world in five legs over the course of four to six days.

Here, an artist renders his impression of what the Solar Impulse might look like once it takes to the skies.